a) Field of the Invention
The invention is directed to a device for heating lock elements in aircraft, in particular to prevent icing of door locks and emergency slide locks.
b) Description of the Related Art
The lock of emergency exits, particularly those with inflatable emergency slides, is subject to special requirements to ensure the safety of passengers during landing and in emergency situations.
On one hand, it is not possible to provide thermal insulation at the aircraft floor in the lower door area because of the space that must be kept clear on the outer side for emergency slides, so that the lock elements would assume the outside temperature during flight at an altitude of several thousand meters, ice up without heating, and accordingly freeze solid. Further, the locks are exposed to extreme changes in temperature (up to 100 Kelvin) during the course of each flight. On the other hand, the lock elements for receiving the door locking bolts are located directly in the access area of the exit and therefore may have only a minimum structural height and are subject to high mechanical and chemical loading (e.g., chemical cleaning and deicing agents).
Current state of the art primarily employs hot air blowers at the lock elements of exits with emergency slides, since there is usually no space for thermal insulation and hot air supply lines or direct heaters at the lock elements below the aircraft flooring in the door or emergency slide area. However, due to the fact that the door locks are connected virtually directly to the aircraft skin, the air flow of the hot air blower must have a considerable temperature and flow rate in order to safely prevent icing of the door lock. However, air flows with temperatures greater than 45° C. and high airflow speeds are highly unpleasant when coming into contact with human skin and lead to unwanted heating of room air and drying of the air in continuous operation. In order to minimize these side-effects while nevertheless safely eliminating icing depending on the outside temperature, the hot air blowers would have to be controlled by sensors which can operate in an optimal manner only in direct contact with the lock element. Further, hot air blowers with alternating thermal loading are relatively prone to malfunction and are far less effective than a direct heating of the lock elements by heat conduction and heat radiation. However, ceramic surface heaters have not been successful as direct heating up to this point because of a partly indefinable thermomechanical and chemical requirement profile during flying operation due to unacceptable failure rates (particularly due to cracking caused by alternating mechanical and thermal loads in conjunction with chemical influences).